Sadegh Kamaei Bahmaei

Ferroelectric Junctionless Double-Gate Silicon-On-Insulator FET as a Tripartite Synapse

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Ali Saeidi, Igor Stolichnov

In this work, we report the concept and experimentally demonstrate the first tunable ferroelectric (Fe) junctionless (JL) transistor (Fe-JLFET), capable of emulating the functionality of biological tri-partite synapses, which is an artificial three-terminal synapse with unique back gate high tuning of the post-synaptic current (PSC). Our device consists of a double-gate 11nm-thin film Fe-JLFET with 10nm Si-doped HfO2 ferroelectric, mimicking the functionality of a tripartite synapse. The gradual ferroelectric switching is exploited to fully reproduce the synaptic plasticity. The back-gate voltage emulates the function of an astrocyte, being used to tune the synaptic weight by more than 400x. Compared to other implementations, the newly proposed tripartite Fe-JLFET synapse device shows simplicity in fabrication, extended programmability, and robustness. We report plasticity until 2000 cycles of operation. Overall, this device concept is promising for CMOS-compatible energy-efficient implementation of future neuromorphic ICs.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2023

Extended gate field-effect-transistor for sensing cortisol stress hormone

Sayedeh Shirin Afyouni Akbari, Luca Capua, Hoël Maxime Guérin, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Shokoofeh Sheibani, Junrui Zhang

Cortisol is a hormone released in response to stress and is a major glucocorticoid produced by adrenal glands. Here, we report a wearable sensory electronic chip using label-free detection, based on a platinum/graphene aptamer extended gate field effect transistor (EG-FET) for the recognition of cortisol in biological buffers within the Debye screening length. The device shows promising experimental features for real-time monitoring of the circadian rhythm of cortisol in human sweat. We report a hysteresis-free EG-FET with a voltage sensitivity of the order of 14 mV/decade and current sensitivity up to 80% over the four decades of cortisol concentration. The detection limit is 0.2 nM over a wide range, between 1 nM and 10 mu M, of cortisol concentrations in physiological fluid, with negligible drift over time and high selectivity. The dynamic range fully covers those in human sweat. We propose a comprehensive analysis and a unified, predictive analytical mapping of current sensitivity in all regimes of operation. Wearable, real-time devices that can monitor hormones are important for personalized healthcare. Here, a platinum/graphene aptamer extended gate field effect transistor is shown to detect cortisol, the primary stress hormone, in physiological fluid.

SPRINGERNATURE2021

Gate energy efficiency and negative capacitance in ferroelectric 2D/2D TFET from cryogenic to high temperatures

Luca Capua, Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Teodor Rosca, Ali Saeidi

We report the fabrication process and performance characterization of a fully integrated ferroelectric gate stack in a WSe2/SnSe2 Tunnel FETs (TFETs). The energy behavior of the gate stack during charging and discharging, together with the energy loss of a switching cycle and gate energy efficiency factor are experimentally extracted over a broad range of temperatures, from cryogenic temperature (77 K) up to 100 degrees C. The obtained results confirm that the linear polarizability is maintained over all the investigated range of temperature, being inversely proportional to the temperature T of the ferroelectric stack. We show that a lower-hysteresis behavior is a sine-qua-non condition for an improved energy efficiency, suggesting the high interest in a true NC operation regime. A pulsed measurement technique shows the possibility to achieve a hysteresis-free negative capacitance (NC) effect on ferroelectric 2D/2D TFETs. This enables sub-15 mV dec(-1) point subthreshold slope, 20 mV dec(-1) average swing over two decades of current, I-ON of the order of 100 nA mu m(-2) and I-ON/I-OFF > 10(4) at V-d = 1 V. Moreover, an average swing smaller than 10 mV dec(-1) over 1.5 decades of current is also obtained in a NC TFET with a hysteresis of 1 V. An analog current efficiency factor, up to 50 and 100 V-1, is achieved in hysteresis-free NC-TFETs. The reported results highlight that operating a ferroelectric gate stack steep slope switch in the NC may allow combined switching energy efficiency and low energy loss, in the hysteresis-free regime.

NATURE PORTFOLIO2021

Intrinsic switching in Si-doped HfO2: A study of Curie-Weiss law and its implications for negative capacitance field-effect transistor

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Teodor Rosca, Ali Saeidi, Igor Stolichnov

HfO2-based ferroelectrics are considered a promising class of materials for logic and memory applications due to their CMOS compatibility and ferroelectric figures of merit. A steep-slope field-effect-transistor (FET) switch is a device for logic applications in which a ferroelectric gate stack exploits a stabilized negative capacitance regime capable to differentially amplify the surface potential in a metal-oxide-semiconductor FET structure, resulting in the improvement of the subthreshold swing and overdrive. In a number of relevant studies of negative capacitance, intrinsic (thermodynamic) switching is assumed, since alternative switching scenarios predict undesirable hysteretic responses in logic devices. However, there is little support from the experimental data showing that the polarization reversal in HfO2-based ferroelectrics is really driven by the intrinsic switching mechanism. In this work, polarization hysteresis loops are measured over wide temperature ranges on polycrystalline Si-doped HfO2 (Si:HfO2) capacitors. The analysis herein, which is based on the classic Landau-Ginzburg-Devonshire theory, yields the temperature-dependent dielectric susceptibility values, which fit the Curie-Weiss law. The extrapolated Curie temperature value is in line with the data obtained for other HfO2-based ferroelectrics using different techniques. The work also illustrates a method to evaluate the ferroelectric equivalent negative capacitance value and range of voltages, aiming at study and optimization of a stabilized negative capacitance FET. This study indicates that the intrinsic switching provides an adequate description of the polarization hysteresis in Si:HfO2 films. This confirms the usability of hafnia-based ferroelectrics for negative capacitance logic devices, and the important role that the intrinsic mechanism plays in the dielectric response of these materials.

AMER INST PHYSICS2021

An Experimental Study on Mixed-Dimensional 1D-2D van der Waals Single-Walled Carbon Nanotube-WSe2 Hetero-Junction

Matteo Cavalieri, Mihai Adrian Ionescu, Farzan Jazaeri, Sadegh Kamaei Bahmaei, Benjamin Paul Johanès Gabriel Lambert, Nicolò Oliva, Amin Rassekh, Ali Saeidi

This experimental study investigates a novel multi-functional one dimensional-two dimensional (1D-2D) heterojunction made of two different band-gap semiconductors, i.e. single-walled carbon nanotube (SWCNT) and tungsten di-selenide (WSe2). The proposed ultra-scaled van der Waals junction behaves like a p-type field-effect transistor (FET) or a gated p-n diode, depending upon the gate bias. A detailed physical study of charge transportation mechanism is presented in a wide range of applied potentials. The obtained results are important towards scaling nanoelectronics to atomic thicknesses by means of the 1D-2D hybrid junctions with additional multi-functional solid-state devices.

2020

Intrinsic switching in Si-doped HfO2: A study of Curie-Weiss law and its implications for negative capacitance field-effect transistor

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Teodor Rosca, Ali Saeidi, Igor Stolichnov

AMER INST PHYSICS2021